|Book III Proposition 22|
the angles ABC, BAC, ACB are equal to two right angles;
the angles ABC, ADC are also equal to two right angles.
Similarly we can prove that
the angles BAD, DCB are also equal to two right angles.
the opposite angles of quadrilaterals in circles are equal to two right angles.
Being what it was required to prove.
|Previous Page Return to Propositions Seq.7 Next: III.31|